|MapGazer – Elevation data|
Elevation data for most of the world’s land surface has been available since the 2000 NASA/NGA Shuttle Radar Topography Mission. A conveniently packaged and cleaned-up version of that elevation data can be found on Jonathan de Ferranti’s website, where there is also a simple interactive download interface by Christoph Hormann (see below for details).
MapGazer supports the 3-second-arc data available from that website; you can download the elevation data for the maps you are interested in (see below for details), and then when moving the cursor over a map you should see the elevation as well as the latitude and longitude displayed in the status at the top left of the window (see screenshot).
To copy elevation data to the clipboard, right-click on a point on a map, select Details, then click Elevation to copy the elevation data for that point to the clipboard.
To select the units used for elevations, select Settings → Measurement units on the menu bar; here you can choose any or all of Metric, Statute (customary), or Nautical units.
Sample map and elevation data
The MapGazer package includes a sample map (MapGazer\MGMaps\SampleMap) and also some sample elevation data that includes the area of that map (MapGazer\elevation3\samples\N43W005.hgt). If you load the SampleMap and move the cursor over the map, you should see elevations appear, similar to the screenshot.
Downloading elevation data for your maps
Clicking on the Download data: ... 3″ link on the page linked above takes you to the the selection map for 3″ elevation data. Each of the smaller darker-blue rectangles on that map represents a 6°×4° area. If you move the cursor over a rectangle you’ll see the “name” of that rectangle (e.g., the one over northwest Spain is ‘K29’). Left-clicking on a rectangle will initiate download of the data (e.g., K29.zip).
After download, the zip file should be unzipped into the MapGazer\elevation3 folder; this should create a folder of the same name as the zip file, and in that folder there will be from one to 24 data files (data files that are wholly sea level are omitted), each covering one degree latitude and longitude and named with its coordinates (for example, one of the northwest Spain files would be MapGazer\elevation3\K29\N42W007.hgt). Do not change either the folder name or the file name, because MapGazer would then not be able to locate the data.
Once the data file is unzipped the elevation should appear (similar to that shown in the screenshot above) whenever the cursor is moved over the corresponding area.
Accuracy of elevation data
The accuracy of elevation data varies (for more information, see the ViewfinderPanoramas dem3 page). Note also that the elevation data is taken from a grid of points 3 seconds of arc (up to 92.5 metres) apart. MapGazer interpolates between these points, but if the points straddle a narrow feature or are on rugged terrain, for example, the elevation shown may not match spot heights and contours shown on the map. Many maps, too, have inaccurate heights and contours.
|MapGazer and these web pages were written by Mike Cowlishaw; Please send me any corrections, suggestions, etc.|
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This page was last updated on 2016-10-22 by mfc.